Sorry to have to do this but I really am interested, after looking at a review of the new D300 it seems that Nikon are taking a different approach to noise compared to Canon
There is nothing new here. Canon leaves the "black current" in the raw data and it's the task of the raw processors to remove it. Nikon records the "amended" data.
It is important to understand, that
1. ACR performs some small noise reduction even if NR is turned down. This is new in version 4; after lots of complains that ACR removes fine details, this inherent noise reduction has been reduced in 4.3 (or in 4.2), but not fully eliminated. ("Inherent", for this NR is part of the demosaicing.);
2. ACR's processing of the black current information is suboptimal, to say the least; the customary horizontal (in landscape orientation) streaks in dark images are the product of ACR's approach. DPP makes it better.
So, your choice of raw processor makes a greater difference for the Canon shots than for Nikons.
I've never liked the soft, almost smeared images canons have produced and it seems that Nikon have produced a camera with more "grain" and less smearing
Did you make comparable shots? Do you mind uploading them?
I suggest an extra test. I am just evaluating such shots from Canon 350D, 20D, 40D and probably more.
1. Cover the lens very tightly with the cap, or use the body cap.
2. Adjust the shutter to 5sec (5sec, so that it be comparable with the other shots I am collecting).
3. Cover the viewfinder tightly and shoot.
4. Upload the raw files.
You may want to do the same in room temperature and with a cold camera. I did not find the difference with the 40D relevant.